Conventional starting drive gears for small, single engine aircraft typically include a drive gear which rotates in response to the starting motor to turn a smaller diameter shaft which is welded to and projects from the center of the drive gear. The shaft is surrounded at its opposite end by a sprag arrangement and an idler gear. Thus, in this arrangement, a relatively small diameter shaft is used to turn the idler gear. This type of arrangement typically has a short life span as a result of rapid deterioration of the sprag. This deterioration is believed to be caused by the stresses placed upon the sprag in transferring rotation from the small shaft to the larger idler gear.
For example, it has been applicant's experience that the starter drive gear for a Cessna 150 has a life of about 350 hours when used extensively by student pilots, whereas the engine time between overhauls is about 2000 hours. Thus, such engine uses about six starter drive gears before an overhaul is needed. Having a starter drive fail in a Cessna 150 is most undesirable because it is connected directly to the crankshaft. If the starter drive freezes, it will try to rotate the starter motor and will likely destroy it, as well. If a starter gear fails when the engine is idling, as on the short-final leg of a landing, the starter gear may stop an engine. This is most disconcerting to any pilot, and especially to student pilots who frequently fly Cessna 150 airplanes. Also, during training exercises, engines are often intentionally turned off. If the starter drive has failed, the engine may be difficult to restart. For all of these reasons, the failure rate of conventional starter drives is not acceptable, and a more reliable mechanism is needed.
It is an object of the present invention to provide a new and improved engine starter drive.
Another object of the present invention is to provide an engine starter drive of the character described which allows the starter motor to more easily turn the crankshaft of the engine to be started.
Still another object of the present invention is to provide an engine starter drive of the character described which is uncomplicated in configuration.